Numerous devices are now offered with near field communication functions. The most widespread are mobile telecommunication devices (mobile telephones or smartphones), which are increasingly often equipped with a near field communication interface, generally dubbed an NFC router, endowing the telephone with additional functionalities. NFC routers allow a mobile device to operate either in card mode or in reader mode. In card mode, the device has the functions of a contactless communication card. In reader mode, the device has the functions of a contactless card reading and/or writing station.
In reader mode, the device uses its rechargeable battery to emit a high-frequency field able to be picked up by another device operating in card mode.
In card mode, the mobile communication device is able to operate by being powered by the field radiated by a station with which it communicates and without resorting to the energy of the battery of the device. This makes it possible, in particular, to endow a mobile telephone with functions similar to those of contactless cards even though the telephone is discharged or turned off. In recent devices, the device can also operate in card mode by using the battery of the device, the electromagnetic field being used for communication.
The battery of the device is generally charged by being hooked up, by way of a charger, to the electrical distribution network, to a dynamo, to a solar panel, etc.
More recently, NFC devices equipped with batteries have begun to appear, the batteries of which are recharged in near field, using a different frequency band for recharging than the frequency band used for communications.